1. Field of the Invention
This invention relates to a water pump apparatus, and more particularly to a water pump apparatus which is utilized in an internal combustion engine of a water cooled type.
2. Description of the Related Art
In a conventional apparatus of this type which is published as Japanese Laid Open No. 61(1986)-1819 and shown in FIGS. 3, 4, and 5, a transmitting mechanism T has a drive pulley (driving means) 22 fixedly mounted to one end of a crankshaft 21, a driven pulley (driven means) 24 fixedly mounted to one end of a rotatable valve camshaft 23, and an endless timing belt 25 comprising valve timing means and extending between both pulleys 22, 24. Power is transmitted from the crankshaft 21 to the rotatable valve camshaft 23 via the transmitting mechanism T. The diameter of the drive pulley 22 and the drive pulley 24 are such that the rotational speed of the valve camshaft 23 is one half of the rotational speed of the crankshaft 21.
The other end of the valve camshaft 23 (end opposite to the transmitting mechanism T) is integrally formed with a connecting terminal 23a for connecting with a connecting terminal 31a integrally formed on a pump shaft 31 of a water pump 30. The water pump 30 is thus connected to the valve camshaft 23 by the connecting terminal 31a, and the rotational axis of the pump shaft 31 is coaxial with the rotational axis of the valve camshaft 23. The pump shaft 31 is supported by a plurality of a ball bearing 32 and is lubricated by engine oil.
In the above-mentioned conventional apparatus, the rotational speed of the water pump 30 is changed by the drive and driven pulley ratio to be one half of the crank rotation speed. Accordingly, the water pump 30 must be large in size in order to maintain sufficient flow volume upon increasing demand. Further, since the pump shaft 31 is supported by a ball bearing 32, the outer diameter of a bearing portion becomes larger. Furthermore, the pump shaft 31 and the valve camshaft 23 are coaxially arranged on the same line, so that they are axially extended, and a L-shaped lubricating passage 33 and seal mechanism 34 are required. As a result, there is a problem that an adequate degree of miniaturization cannot be easily attained. There is also a problem that various vehicle and engine specifications require a large variety of water pumps, each having slightly different discharge volume requirements.